1. Field of the Invention
The invention relates to animal watering valves and, more particularly, relates to animal actuated valves for use by mice, rats, and other relatively small laboratory animals or other animals.
2. Discussion of the Related Art
Animal actuated watering valves are well known. One such valve is disclosed in U.S. Pat. No. 5,065,700 which issued to Cross on Nov. 19, 1991 (the Cross patent). The valve disclosed in the Cross patent employs a housing having an inlet and an outlet connected by an elongated longitudinal bore, a valve element located adjacent the inlet, and an elongated actuating lever or valve stem which extends through the bore, which projects out of the outlet, and which, when deflected by an animal, opens the valve element to permit the passage of fluid through the valve housing. A movable shield or shutter member is provided adjacent the outlet to inhibit the animal from stuffing bedding material or other debris into the outlet and thus inhibits the valve from being unintentionally lodged in its open position.
The watering valve disclosed by the Cross patent suffers from several drawbacks and disadvantages. For instance, the shutter or shield is rigid and thus 1) must move with the stem or actuating lever to permit valve opening, and 2) is incapable of deflecting upon being contacted by an animal or a foreign object. The shield is thus subject to corrosion and jamming which may inhibit or even prevent valve opening or which may cause the valve to stick in its open position.
Some of the problems associated with the valve disclosed by the Cross patent can be alleviated by providing a deformable shield for the valve. For instance, U.S. Pat. No. 5,501,177 to Edstrom (the Edstrom patent) discloses an animal watering valve that employs a resilient elastomeric shield at the distal end of the valve which corresponds to the shield of the Cross patent but which is not subject to the corrosion and sticking problems discussed above with respect to the Cross patent. The shield takes the form of a unitary elastomeric generally cup-shaped member including a cylindrical body, a flange extending radially outwardly from an upstream end of the body, and a membrane covering a downstream end of the body. The flange is clamped between two cooperating members of a housing of the valve, and the membrane has a central aperture through which a stem of the valve passes. The periphery of the body is located relatively close to the periphery of the surrounding portion of the bore such that, when the valve stem is actuated, the outer radial edge of the membrane abuts the peripheral surface of the bore to arrest additional membrane movement. Continued valve stem deflection distorts the membrane to enlarge a gap between the valve stem and the periphery of the membrane aperture so as to permit unobstructed water flow out of the valve. The resilient distortion of the membrane also helps bias the valve stem towards its undeflected or closed position. This arrangement, though satisfactory, exhibits significant drawbacks and disadvantages.
For example, the shield may be pinched or damaged during assembly due to the fact that the upstream flange is clamped between the body and the guard during valve assembly. Moreover, the relatively close proximity of the shield to the periphery of the bore permits only limited membrane movement before the shield contacts the bore, after which the membrane can move only through membrane distortion. As a result, it has been discovered that bedding or other materials can become lodged between the valve stem and the periphery of the membrane aperture so tightly that the valve stem may be lodged in its deflected or open position. Moreover, under some circumstances, it may be possible for an animal to bite into the shield and destroy it. In addition, the biasing or return forces imposed by the deflected shield, though relatively small, are more than insignificant and may hinder valve actuation by weanling mice or other weak animals.